In universal mobile telecommunications system (UMTS) release 6, a new channel was introduced in the uplink (UL): the enhanced dedicated channel (E-DCH). The E-DCH is an UL-only transport channel mapped to the enhanced packet data physical channel (E-PDPCH). Associated with the E-DCH is the enhanced dedicated physical control channel (E-DPCCH), which is a UL physical channel used to transmit control information. The E-DCH provides higher capacity, higher throughput and reduced delay when compared with the traditional dedicated channels (DCHs). The E-DCH is only applicable to UMTS terrestrial radio access (UTRA) frequency division duplex (UTRA FDD).
The enhanced medium access control (MAC-e) is a new entity that handles the E-DCH transport channel. As in traditional DCHs, the E-DCH is configured with specific E-DCH transport format combinations (E-TFCs). However, as opposed to receiving a set of allowed transport formats from a radio resource control (RRC), the MAC-e is configured to use a set of transport formats based on pre-defined tables.
There are four of the above referenced pre-defined tables in the 3GPP standard. Two tables are used for a 2 ms transmission time interval (TTI), and two tables are used for a 10 ms TTI. A radio resource control (RRC) configures the TTI length, and also, determines which of the two tables the MAC-e should use when selecting a transport format. Table 1 shows a 10 ms TTI E-DCH transport block (TB) size table.
TABLE 1TB IndexTB Size (bits)01811202124313041355141614771538159916610172111801218713195142031521116220172291823919249202592127022281232932430525317263312734428359293743038931405324223344034458354773649737517385393956140584416084263443660446874571646745477764880949842508775191352951539915410325510745611195711655812145912646013166113716214286314876415496516136616806717496818226918977019767120587221437322327423257524217625217726267827357928488029668130898232178333508434898536348637848739418841058942759044529146369248289350299452379554549656809759159861619964161006682101695910272471037547104786010581861068525107887810892461099629110100281111044411210877113113281141179711512286116127951171332511813877119144531201505112115675122163251231700112417706125184401261920412720000
The main difference between the E-DCH transport format set and the traditional transport format set, (other than the sizes being pre-configured), is that these tables are very large, whereby each table contains more than 120 TB sizes.
The rules for E-TFC selection are described in the UMTS standards, (e.g., TS 25.331). According to these rules, the E-TFC restriction procedure shall always be applied before the E-TFC selection process. The E-TFC restriction procedure is used because a wireless transmit/receive unit (WTRU) is not allowed to exceed a maximum allowed UL transmission power when transmitting in the UL channels. During the restriction procedure which is performed at every TTI, a WTRU calculates the amount of power required to transmit a given E-TFC. The WTRU then calculates the estimated power leftover from TFC selection when the dedicated physical data channel (DPDCH) is present, and it calculates the leftover power from a high-speed dedication physical control channel (HS-DPCCH) transmission, and a high-speed dedicated physical common control channel (DPCCCH) transmission. If the required power to transmit a given E-TFC is greater than power available to the WTRU, it implies that the E-TFC that requires too much power may not be supported at a given TTI. These E-TFCs are considered to be in a blocked state. The particular E-TFCs that are in a blocked state may vary at every TTI, depending on the level of power consumption by the other UL channels.
The UTRAN should ensure that the ordering of the enhanced transport format combination indicator (E-TFCI) table is in increasing transmission power, by correctly setting of reference E-TFCI power offsets (which are then used to calculate βed,j, βed,C,j and βc,C). This guarantees that the elements of an E-TFC table are ordered in terms of power requirement. Therefore, in order to determine which E-TFC is blocked, the WTRU starts searching from the bottom of the table (largest TB size) and proceeds up the table, until it finds an E-TFC that is not blocked (i.e., unblocked). Once the WTRU finds an unblocked E-TFC it can terminate the search because it can assume that, if an E-TFC of a particular TB size is not blocked, then all E-TFCs with smaller TB sizes are not blocked. Similarly, if an E-TFC of a particular TB size is blocked, then the WTRU can assume that all E-TFCs with larger TB sizes are also blocked.
However, a problem arises with the introduction of the Maximum Power Reduction (MPR) element. A WTRU may reduce the maximum allowed transmit power by the E-TFC MPR values specified in the 3GPP, which are shown in Table 2. With the introduction of MPR, the selection of a supported E-TFC based on the power limitation becomes a more complex and time-consuming procedure. Since the E-TFC MPR values are dependent on the number of codes and the minimum spreading factor allowed to be used, and the MPR values are not directly proportional to the required power of each E-TFC, there will be holes in the E-TFC table. When there are holes, if a given E-TFC is not blocked, that does not necessarily mean that all E-TFCs with smaller TB sizes are also not blocked. So, even though the ETFCs are listed in order of increasing transmission power, because the maximum allowed power (PMaxj) varies for each ETFC, and the variation is not directly proportional to the required power of each ETFC, then the assumption that if a given E-TFC of a particular TB size is not blocked then all E-TFCs with smaller TB sizes are also not blocked, does not necessarily hold true. Similarly, if a given E-TFC is blocked, that does not necessarily mean that all E-TFCs with larger TB sizes are also blocked. Table 2 shows an example of an E-TFC-MPR used for E-TFC selection. This creates holes in the table, which means that every ETFC in the table needs to be inspected to verify if they are in a blocked state.
It would therefore be desirable to handle such holes and avoid having to search the entire table by performing faster/smarter searches that do not require searching the entire table.
TABLE 2Inputs for E-TFC selectionE-DPDCHE-TFC-CaseβcβhsβdβecβedSFminNcodesMPR (dB)1>000>0>0≧410.252>0≧00>0>0240.503>00>0>0>0≧410.754>0>0>0>0>0≧411.505>0≧0>0>0>0420.756>0≧0>0>0>0220.50Note:For inputs {βc, βhs, βd, βec, βed, SFmin, Ncodes} not specified above the E-TFC-MPR (dB) = 0